Glazing with variable absorbing power

ABSTRACT

The invention concerns glazing sheets with variable absorbing power. The glazing comprises two transparent walls providing an inter-wall space containing one of the two following fluids: either a first transparent fluid, such as air; or a second transparent fluid, absorbing solar energy over a very large part of the spectrum, in particular liquid water or liquid water with added alcohol. The glazing further compromises a circuit for discharging energy in the form of a bead, located at its periphery, preferably consisting of a heat pip-exchanger. The glazing also comprises an apparatus for filling up or emptying the inter-wall space, as well as flexible elements for absorbing the second fluid expansion depending on temperature. The glazing can in particular be used for producing car windows.

The present invention relates to glazings.

Enclosures closed by transparent glazings receive strong solar loads,especially in summer. This is notably the case for the passengercompartment of a vehicle, and also for horticultural greenhouses andhouse walls exposed to the South or East-West. The temperature insidethe enclosure increases and becomes too high for the objects or theplants which are placed therein or for persons who are in there or whoare induced to penetrate therein.

It is known that this drawback is partly overcome by staining the glassglazing so that a fraction of the solar load is reflected, withouthowever affecting the transparence and the passengers' visibility to theoutside of the vehicle. Windows with double glazing are also knownwherein the internal space thereof is filled with gas having a lowthermal conductivity at a relatively low pressure. It is thus possibleto substantially reduce heat transfer by convection. U.S. Pat. No.4,928,448 describes such a device. However, thermal isolation obtainedin this way does not provide an obstacle to the solar load transferredthrough radiation.

Double glazing windows are also known. Depending on insolation, eitheran insulating liquid is introduced between the walls or the liquid isemptied from the inter-wall space which contains it. U.S. Pat. No.5,787,652 describes such a vehicle window. The radiated heat is absorbedby the insulating liquid which transfers it to the inside of the vehicleby conduction and by convection.

The object of the present invention is to solve the posed problem bylimiting the effects of radiated solar loads, notably in the case of astopped vehicle when air-conditioning is no longer running. The presentinvention also aims at finding a remedy for the posed problem withoutaffecting the glazing's transparence.

The glazing according to the invention has variable absorptivity. Itcomprises two transparent, notably glass walls. Other transparentmaterials other than glass may also be contemplated, notably syntheticplastics. These two walls provide an inter-wall space. Depending on theindividual case, the latter contains

either a first transparent fluid, notably a gas such as air,transferring solar energy in the transparence wavelength bands of saidwalls,

or a second fluid transparent in the visible portion of theelectromagnetic spectrum, absorbing solar energy on a very wide portionof the electromagnetic spectrum, notably water in the liquid state orwater in the liquid state with alcohol added.

In the first case, the glazing's transparence in the visible portion ofthe electromagnetic spectrum is not affected and the glazing transfersthe major portion of the solar load which it receives.

In the second case, the glazing absorbs the major portion of the solarenergy which it receives, while remaining transparent in the visibleportion of the electromagnetic spectrum. Indeed, water in the liquidstate has the property of transparence, notably when it is in a thinlayer under thicknesses from 1 to 2 millimeters. On the other hand,water in the liquid state has properties close to those of a black bodyabsorbing solar radiations. Water in the liquid state as a thin layerdoes not provide an obstacle to transparence and furthermore, the smallthickness of inter-wall space blocks convective motions. Hence, in thissecond case, the glazing is a radiation shield.

According to another essential characteristic feature of the invention,the glazing comprises a circuit for discharging energy located at itsperiphery. Preferably, the circuit for discharging energy located at theperiphery of the glazing is a bead-shaped exchanger, with a heat pipeeffect. Also advantageously, the second fluid absorbing solar energy isunder its vapor pressure. It vaporizes and condenses in the free spacewithin the bead. Heat energy absorbed by said second insulating fluid(in the sense of the present description, the expression “insulatingfluid” refers to an absorbing fluid or liquid) is thus dissipated at theperiphery of the glazing towards the outside. The exchange surface iscalculated in order to discharge heat towards the outside, by convectionand conduction.

In the configuration of the second case, when the interwall space isfilled with the insulating liquid, the glazing is thus well adapted fora stopped vehicle receiving a high solar load. Although the airconditioning is no longer running as the engine is stopped, thetemperature inside the vehicle remains moderate. The passenger which nowclimbs into his vehicle no longer has to wait for the air-conditioningto be running again at its standard rating in order to feel thewell-being of a moderate temperature.

Nevertheless, the driver may consider that the shield of water in theliquid state affects his/her visibility and may prefer to drive hisvehicle while benefiting from maximum visibility, that obtained in thesituation where the fluid filling the inter-wall space is air, or wherethe second fluid is under its vapor pressure. The effect of the solarload is then compensated by the air-conditioning which has been able tostart after starting the engine.

Preferably, according to a complementary feature of the presentinvention, the glazing further includes means for filling or emptyingthe inter-wall space in order to fill said space with said second fluidwhich absorbs solar energy or, according to the case, to empty saidspace of said second fluid and to substitute said first fluid for it.

Also preferably, the glazing according to the invention is such that theperiphery of the glazing includes an expansion volume for absorbingexpansions of the second fluid depending on the temperature. Thisexpansion volume may notably be achieved by means of free volume insidethe bead located at the upper portion of the glazing.

Advantageously, the thickness of the inter-wall space is larger than orequal to 1 millimeter and less than or equal to 2 millimeters. Such athickness is sufficiently large so that water in the liquid state mayact, with the properties of a back body, it is sufficiently small forblocking convective motions.

The glazing according the present invention may be applied to thethermal preconditioning of the passenger compartment of a vehicle, tothe creation of a window in dwelling premises, to the creation ofgreenhouses.

Other characteristics and advantages of the invention will becomeapparent upon reading the description of alternative embodiments of theinvention, given as an indicative and non-limiting example, and of:

FIG. 1 which shows the overall diagram of the framework of a motorvehicle equipped with double wall and water sheet glazing, FIG. 1 alsoshows an alternative embodiment of a filling and emptying system for theinter-wall space,

FIG. 2 which shows an enlarged sectional view of the front glazing ofthe vehicle along a vertical plane A—A, when the heat energy absorbingliquid is in presence of air,

FIG. 3 which shows an enlarged sectional view of the front glazing ofthe vehicle along a vertical plane A—A, when the heat energy absorbingliquid is under its vapor pressure.

FIGS. 1, 2 and 3 will now be described.

The glazing 1 according to the invention has variable absorptivity. Itcomprises two transparent glass walls 2, 3. Both these walls provide aninter-wall space 4 with a thickness from 1 to 2 millimeters. Dependingon the individual case, the latter contains,

either a first transparent fluid, notably a gas such as air,transferring solar energy in the transparence wavelength bands for saidwalls,

or a second fluid 5 transparent in the visible portion of theelectromagnetic spectrum, absorbing solar energy on a very wide portionof the spectrum, notably water in the liquid state or water in theliquid state with added alcohol.

In the case illustrated in FIG. 2, the second fluid 5 is water in thepresence of air, in this case the first fluid is air. In the caseillustrated in FIG. 3, the second fluid 5 is water under its vaporpressure, in this case the first fluid 5 is steam under a low (absolute)pressure, typically 0.04 bar at 30° C. (which corresponds to thesaturation vapor pressure or water vapor pressure).

When the inter-wall space 4 is filled with air or steam under its vaporpressure, the transparence of the glazing is not affected and theglazing transfers the major portion of the solar load which it receives.

When the inter-wall space 4 is filled with water, the glazing absorbsthe major portion of the solar energy which it receives, while remainingtransparent in the visible portion of the electromagnetic spectrum.Glazing 1 is a radiation shield in this configuration. Indeed, water inthe liquid state has the property of transparence when it is in a thinlayer under thicknesses of 2 millimeters. On the other hand, water inthe liquid state has the properties of a quasi black body absorbingcertain solar radiations, so to speak. Water in the liquid state as athin layer does not provide an obstacle to transparence in the visibleportion of the electromagnetic spectrum and furthermore, the smallthickness of the inter-wall space blocks convective motions.

Although air-conditioning is no longer running when the engine isstopped, the temperature inside the vehicle remains moderate. Thepassenger who now climbs into his vehicle no longer has to wait for theair-conditioning to be running again at its standard rating in order tofeel the well-being of a moderate temperature.

In certain cases, the driver may consider that the shield of waterfilling the inter-wall space 4 affects his visibility. Now, he prefersdriving his vehicle while benefiting from maximum visibility. For thispurpose, he will substitute air for the fluid in the liquid phasefilling the inter-wall space or else he will substitute this same fluidin the vapor phase for it. To do this, the driver starts pump 20. Thispump includes a set of valves which allows the flow of fluids to bereversed in the ducts 21 c from pump 20 to the liquid tank 22 as well asin ducts 21 a from pump 20 to the glazing and notably in ducts 21 b frompump 20 to glazing 1 b of the right front door. The pump sucks in theliquid which is contained in the inter-wall spaces of glazings 1 a and 1b and generates sufficient depression in order to substitute a vaporphase of this same liquid for it or to enable air to enter through duct6, after opening the valve (not shown) placed on this duct.

Conversely, on stopping the vehicle, the driver starts pump 20 byreversing the direction of the valves (this operation may beautomatically controlled by turning the ignition key). The pump sucks inthe liquid contained in tank 22 and injects it, through ducts 21 a and21 b, into the inter-wall space of glazings 1 a and 1 b.

When the heat energy absorbing liquid 5 is discharged, the effect of thesolar load is compensated by the air conditioning which has been able tostart after starting the engine.

Glazing 1 includes at its upper periphery, a mechanical bead 8 enablingthe glazing to be mounted on the framework of the vehicle. Inside thisbead 8, a free expansion volume 7 is provided. Thus, the liquid 5 mayfreely expand depending on the temperature.

The glazing also includes at its periphery, a circuit for dischargingheat energy absorbed by liquid 5. This energy discharge circuit isprovided in the mechanical bead 8.

The energy discharge circuit will now be described with reference toFIG. 3, notably when liquid 5 is under its vapor pressure. In thisfigure, the main components of the glazings as described earlier arerecognized, particularly walls 2 and 3, the inter-wall space 4containing liquid 5, the mechanical bead 8 at the periphery of theglazing.

Liquid 5 is introduced into the inter-wall space 4 at its vaporpressure. The vapor phase is located above the filling level 9 in thefree volume 7 of the mechanical bead 8. After filling, duct 6 betweenfree volume 7 and tank 22 is closed by a valve. Pump 20 is an air pump.Discharge of the heat absorbed by liquid 5 occurs by evaporation at theliquid-vapor interface 9.

In the alternative illustrated in FIG. 3, the energy discharge circuitcomprises an exchanger 8 a with a heat pipe effect located in thethickness of the upper mechanical bead 8 of the glazing. It may alsocomprise a flexible exchanger 8 a covering the internal surface of theupper mechanical bead 8 of the glazing. Vapor contained in free space 7will condense at the exchanger 8 a with a heat pipe effect. Heatreceived by the exchanger 8 a during condensation of the vapor phase maybe discharged either towards the outside directly (in the ambient air)or towards an auxiliary heat exchanger by means of a circuit assisted bya pump.

An energy discharge circuit achieved by means of a mechanical bead 8including fins on the outside may also be used. The exchange surface ofthe mechanical bead 8 is calculated in order to discharge heat into theatmosphere by conduction and convection. Heat energy absorbed by fluid 5is thus dissipated at the periphery of the glazing towards the outside.

The energy discharge circuit will now be described with reference toFIG. 2, notably when liquid 5 is at atmospheric pressure in the presenceof air. In this case, a heat pipe effect energy discharge circuit mayalso be used in the same way as described with reference to FIG. 3. Heatabsorbed by liquid 5 is transferred through simple convection to theheat pipe effect exchanger 8 a. A mechanical bead including fins on theoutside may also be used. Heat energy absorbed by fluid 5 is thusdissipated at the periphery of the glazing towards the outside. However,thermal exchange is less efficient than in the case when the absorbingliquid 5 is under its vapor pressure. The temperature of liquid 5 willthen be in this case significantly higher.

During the emptying phase for the absorbing liquid, air will besubstituted for liquid sucked in by the pump 20, by its penetrationthrough duct 6, in the same way as described above.

The configuration which applies a liquid, notably water under its vaporpressure or in presence of air in the inter-wall space of adouble-walled glazing, transferring the absorbed heat to an energydischarge circuit located at the periphery of the glazing, notably madeas a heat pipe effect exchanger, may be interesting per se. In certainalternative embodiments, it is not absolutely necessary to substitutegas or a vapor for the liquid filling the space in order to improvevisibility.

What is claimed is:
 1. A glazing with variable absorprivity comprising:two transparent walls spaced apart from each other to provide aninter-wall space, the inter-wall space containing one of the twofollowing fluids: a first transparent fluid transferring solar energy inthe transparence wavelength bands of said walls, or a second fluidtransparent in the visible portion of the electromagnetic spectrum whichabsorbs solar energy on a wide portion of the spectrum; and an energydischarge circuit located at the periphery of the glazing.
 2. Theglazing according to claim 1 wherein the second fluid is at its vaporpressure.
 3. The glazing according to claim 1, wherein the energydischarge circuit located at the periphery of the glazing is abead-shaped exchanger.
 4. The glazing according to claim 1, furthercomprising: means for filling or emptying the inter-wall space in orderto fill said space with said second fluid absorbing solar energy or toempty said space of said second fluid and to substitute said first fluidfor said second fluid.
 5. The glazing according to claim 1, wherein theperiphery of the glazing includes an expansion volume for absorbingexpansions of the second fluid according to the temperature.
 6. Theglazing according to claim 1, wherein the thickness of the inter-wallspace is larger than or equal to 1 millimeter and less than or equal to2 millimeters.
 7. The glazing according to claim 1, wherein the firstfluid is a gas.
 8. The glazing according to claim 7, wherein the gas isair.
 9. The glazing according to claim 1, wherein the second fluidcomprises water in a liquid state.
 10. The glazing according to claim 1,wherein the second fluid comprises water in a liquid state with alcoholadded.
 11. The glazing according to claim 3, wherein the bead-shapedexchanger is a heat pipe exchanger.
 12. A vehicle comprising a glazingthat includes two transparent walls spaced apart from each other toprovide an inter-wall space, the inter-wall space containing one of thetwo following fluids: a first transparent fluid transferring solarenergy in the transparence wavelength bands of said walls, or a secondfluid transparent in the visible portion of the electromagnetic spectrumwhich absorbs solar energy on a wide portion of the spectrum; and anenergy discharge circuit located at the periphery of the glazing.
 13. Adwelling comprising at least one window having a glazing that includestwo transparent walls spaced apart from each other to provide aninter-wall space, the inter-wall space containing one of the twofollowing fluids: a first transparent fluid transferring solar energy inthe transparence wavelength bands of said walls, or a second fluidtransparent in the visible portion of the electromagnetic spectrum whichabsorbs solar energy on a wide portion of the spectrum; and an energydischarge circuit located at the periphery of the glazing.
 14. Agreenhouse comprising a glazing that includes two transparent wallsspaced from each other to provide an inter-wall space, the inter-wallspace containing one of the two following fluids: a first transparentfluid transferring solar energy in the transparence wavelength bands ofsaid walls, or a second fluid transparent in the visible portion of theelectromagnetic spectrum which absorbs solar energy on a wide portion ofthe spectrum; and an energy discharge circuit located at the peripheryof the glazing.
 15. A glazing comprising: two transparent walls spacedapart from each other to provide an inter-wall space, said inter-wallspace containing a fluid; and an energy discharge circuit located at theperiphery of the glazing.
 16. The glazing according to claim 15, whereinthe fluid comprises water in a liquid state.
 17. The glazing accordingto claim 15, wherein the fluid comprises water in a liquid state withalcohol added.
 18. The glazing according to claim 15, wherein the fluidis at its vapor pressure.
 19. The glazing according to claim 15, whereinthe energy discharge circuit comprises comprises a bead-shapedexchanger.
 20. The glazing according to claim 19, wherein thebead-shaped exchanger is a heat pipe exchanger.
 21. The glazingaccording to claim 15, wherein the periphery of the glazing includes anexpansion volume for absorbing expansions of the fluid according to thetemperature.
 22. The glazing according to claim 15, wherein thethickness of the inter-wall space is larger than or equal to 1millimeter and less than or equal to 2 millimeters.
 23. A vehiclecomprising a glazing that includes two transparent walls spaced fromeach other to provide an inter-wall space, said inter-wall spacecontaining a fluid; and an energy discharge circuit located at theperiphery of the glazing.
 24. A dwelling comprising at least one windowhaving a glazing that includes two transparent walls spaced from eachother to provide an inter-wall space, said inter-wall space containing afluid; and an energy discharge circuit located at the periphery of theglazing.
 25. A greenhouse comprising a glazing that includes twotransparent walls spaced from each other to provide an inter-wall space,said inter-wall space containing a fluid; and an energy dischargecircuit located at the periphery of the glazing.